1. Field of the Invention
This invention relates to the transdermal delivery of narcotic analgesics. More specifically, the invention relates to pharmaceutical compositions containing as an active ingredient etorphine or an etorphine related analog/derivative in association with a pharmaceutical carrier adapted for topical application to mammalian skin and delivery system for transdermal use of such compositions.
2. Description of the Prior Art
It is generally known and an accepted practice to administer opioid narcotic analgesics such as morphine and morphine related compounds to control chronic pain. Such narcotic analgesics play a prominent role in the control of pain associated with chronic diseases, especially the chronic pain of cancer, and acute pain, especially the acute pain experienced post-operatively. However, such prior art uses of narcotic analgesics are subject to serious problems. In addition to the obvious problem associated with potential abuse and addiction, the oral and parenteral administration of a narcotic analgesic for pain control frequently involve wide swings in the pharmacodynamics of the narcotic drug over each dosing interval. In other words, the peaks and valleys of blood levels of the drug associated with discrete doses leads to patients passing in and out of sedation (euphoria, dysphoria) on the early side and pain on the late side of the dosing interval. Furthermore, analgesic narcotics characteristically have short durations of action, tend to be sedative in pain relieving doses, are inefficiently absorbed orally due to first pass metabolism, tend to depress respiration and tend to be nauseating and/or have other side effects. Surprisingly, very little is reported in the published literature concerning the cytotoxicity of such compounds.
More recently, special interest in the transdermal route of administering narcotics in cancer patients has arisen. In such cases, pain is the most common symptom for which patients seek medical relief and therefore, a more reliable method of delivery and safer route of drug administration to patients are of primary concern. The transdermal delivery of narcotic analgesics, in principle, should have clinical advantages such as (1) it would allow patients to become mobile, (2) it would avoid the necessity of having a sterile syringe, needle, and cleansing of the skin with alcohol or other substance prior to injection as well as avoiding the after pain of injections, (3) it would also avoid the peak and trough phenomenon, and (4) it should reduce the risk of addiction in that a non-euphoric steady state would be maintained rather than the euphoria producing peaks associated with each time the drug is administered parenterally. However, again, very little is known as to the cytotoxicity of narcotic analgesics in transdermal application and in particular, whether or not a reliable and safe transdermal narcotic analgesic therapy exists.